Place roast in slow cooker. Pour entire jar of pepperoncini, including all juice over top of beef. Cook on low for 12-13 hours. Beef should be very tender and shred easily at this point. Shred beef and mix well. Cook on low for another 6-12 hours. For a variation, you may add sliced onions, sliced mushrooms and/or minced garlic at the beginning of cooking time. Serve on rolls, bread, or as it's own entree.